We created a nice extension that adding Previous
and Next buttons on your product pages. It useful for your store because after
applying this module. Customer no need to jump on category page to go next
product they can navigate from button next and back from product page. It help
customer to see all product easily without waste more time. Our all module will
not affect any core file of opencart so it will not issue during updating
opencart.

No Core file Changes
Just VQMOD required

We created an extension that adding Previous and Next product buttons on your product pages in category or without category